1. Field of the Invention
The present invention relates to a driving apparatus of a developing apparatus of a laser printer, copier, or the like, and a developing apparatus using the driving apparatus, and more particularly, to a driving apparatus of a detachable developing apparatus capable of enhancing quality of a printed image by inducing uniform rotation and dampening of vibration even when a photosensitive unit and a developing unit are separately driven, and the detachable developing apparatus using the driving apparatus.
2. Description of the Related Art
In a laser printer, copier, combined printer, or the like, a developing apparatus for printing a processed image on a recording sheet is provided in the shape of a cartridge. In a related art, a photosensitive unit, the surface of which is scanned by a laser so that an electrostatic latent image can be formed on the surface thereof, and a developing unit for supplying toner to the photosensitive unit so that a toner image corresponding to the electrostatic latent image can be formed, are installed together in one cartridge. However, when the photosensitive unit and the developing unit are combined in one cartridge as above-mentioned, there is a problem in which even though the usable life of the photosensitive unit is generally much longer than that of the developing unit, the photosensitive unit must be replaced together with the developing unit when the developing unit reaches the end of its usable life, even if the photosensitive unit operates normally.
In order to solve this problem, as shown in FIG. 1, a structure in which a photosensitive unit 110 and a developing unit 120 are separated and driven separately was proposed. According to such a structure, the photosensitive unit 110 and the developing unit 120 are separately installed at a main body of a printer, copier, or the like, and are driven separately by separate gears. At this time, when the developing unit 120 is pressed toward the photosensitive unit 110 by a force of a spring, or the like with the photosensitive unit 110 fixed to the main body, a photosensitive drum 111 of the photosensitive unit 110 and a developing roller 121 of the developing unit 120 come into contact with each other, and slidably rotate together in their respective directions.
A structure and operation of such a detachable developing apparatus shown in FIG. 1 will be described in detail as follows.
First, a driving force to the photosensitive unit 110 is transferred from a photosensitive drum driving gear 113 to a photosensitive drum gear 112 which forms an image on a recording medium, such as a paper 200. Accordingly, when the photosensitive drum gear 112 rotates, the photosensitive drum 111 joined to the photosensitive drum gear 112 also rotates. On the other hand, a driving force to the developing unit 120 is transferred to the developing roller 121 first, and while a first idle gear 125 rotates according to the rotation of the developing roller 121, a portion of the driving force is transferred to a supply gear 126, and a toner supply roller 122 rotates. In addition, the other portion of the driving force is transferred to an agitator gear 128 via the first idle gear 125 and a second idle gear 127. When the agitator gear 128 rotates, an agitator 123 joined to the agitator gear 128 also rotates, and, accordingly, toner is moved by the agitator 123 toward the toner supply roller 122. Power transfer of the photosensitive unit 110 and the developing unit 120 are done separately, and therefore all the loads applied to respective gears are reduced.
However, when the photosensitive unit 110 and the developing unit 120 are driven separately from each other, there is possibility that a contacting nip depth or width between the photosensitive drum 111 and the developing roller 121 may be uneven. In order to prevent this problem, when the developing unit 120 is pressed by the force of the spring after the developing unit 120 is completely installed at the main body, the axis of the rotating shaft of the developing roller 121 and the axis of the driving shaft of a driving gear 140 supported by the main body must be precisely aligned with each other. However, at least some eccentricity will occur due to tolerance or the like occurring during manufacturing and assembling processes. Therefore, when the driving gear 140 (see FIG. 2) is directly connected to the shaft of the developing roller 121, eccentricity always occurs at the axis between the developing roller 121 and the driving gear 140. When the eccentricity occurs in this manner, the shaft of the developing roller 121 suffers vibrations during the rotation of the developing roller 121. The nip depth between the photosensitive drum 111 and the developing roller 121 is thus uneven, resulting in unstable development nips. Usually, the development nip depth is maintained in the range of about 0.05˜1.15 mm in a nonmagnetic one-component contact development method, and when the development nip depth is greater than the range values, excessive pressure causes toner stress to occur. When the development nip depth is smaller than the range values, the development nip is not formed, and therefore image formation is not possible.
Therefore, as shown in FIGS. 2 and 3, a coupling member 130 is interposed between the developing roller 121 and the driving gear 140 so that the developing roller 121 can stably rotate even when an eccentricity occurs between the developing roller 121 and the driving gear 140 connected to the developing roller 121 to be aligned with the rotation axis of the developing roller 121, and the nip depth between the photosensitive drum 111 and the developing roller 121 can be maintained to be constant. Generally, a method of using the coupling member 130 having a shape shown in FIGS. 2 and 3 is known as the Oldham's coupling method. The Oldham's coupling is a mechanism usually used to smoothly transmit power even when eccentricity occurs between shafts.
As previously described, the driving force to the developing unit 120 is transferred to the developing roller 121 first via the driving gear 140 and the coupling member 130, and, thereafter, is transferred to the toner supply roller 122 and the agitator 123 via the idle gears 125 and 127. However, as shown in FIG. 4, the driving force of a motor pinion gear 160 which rotates at high speed is transferred to the driving gear 140 via a reduction gear 150. That is, speed reduction is performed before the driving force reaches the driving gear 140, and only after the speed reduction is completed is the driving force transferred to the developing unit 120 and the coupling member 130. As shown in FIG. 4, there is no speed reduction between the developing unit 120, the coupling member 130, and the driving gear 140. Therefore, in the conventional art, the load of the developing unit 120 is transferred to the coupling member 130 and the driving gear 140 without being changed. When the unchanged load of the developing unit 120 is transferred to the coupling member 130 and the driving gear 140, an excessive load may be applied to the coupling member 130 and the driving gear 140. Then, friction increases at four sliding slots 138 formed at right angles with one another at the outer circumferential surface of a coupling disc 132 positioned between a coupling gear 131 of the coupling member 130 and a coupling drive 134. Accordingly, since smooth sliding movement of the coupling disc 132 is prevented a problem occurs in which a principal function of the Oldham's coupling is lost.
Therefore, in the conventional art, in order to minimize frictional loads at the four sliding slots 138 formed at right angles with one another at the outer circumferential surface of the coupling disc 132, two pairs of rotation shafts 136 are installed at respective surfaces of the coupling gear 131 and the coupling drive 134 which face the coupling disc 132 to project from the respective surfaces, and to make an angle of 180° with each other on the respective surfaces. Also, sliding rollers 133 are fitted around the respective rotation shafts 136 so as to rotate in the sliding slots 138. Consequently, the structure of the coupling member becomes very complex due to the installation of such sliding rollers 133, and the cost thereof increases due to the installation of the rotation shafts 136 and the sliding rollers 133.